The objective of the proposed study is to acquire information relevant to the structure, function and maintenance of specific plasmids in Streptococcus faecalis. A major focus will concern certain unique aspects of the plasmid pi-AM-alpha-1 pertaining to its ability to amplify its tetracycline(TC)-resistance (TCr) determinant during growth in the presence of TC. Certain features of pi-AM-alpha-1, especially its small size (6 megadaltons), make it amenable to specific types of analyses that would be very difficult with other kn wn amplifiable plasmids (which are an order of magnitude larger in size). The studies will concern the mechanism of gene amplification, and the involvement of the recombination sequence RS1. Certain aspects of plasmid maintenance (replication) relevant to amplification will also be investigated. Studies will also focus on a recently identified multiple resistance plasmid, pi AD2 (determining resistance to erythromycin, streptomycin, and tetracycline), which appears to be involved in the amplification of a chrom somally borne TC - determinant via an integration into the chrom some. Attention will be given to characterizing the nature of this phenomenon and the possible involvement of RS sequences. Studies on this system will have significant bearing on the generality of amplification models proposed for the pi-AM-alpha-1 system.